Congo red

Author: Nat Pernick, M.D. (see Authors page)

Revised: 3 December2015, last major update October 2013

Copyright: (c) 2003-2015,, Inc.

PubMed Search: congo red[title]
Cite this page: Congo red. website. Accessed March 24th, 2018.
Definition / general
  • Also called amyloid stain
  • Must examine stained tissue with standard and polarized light
  • Amyloid under polarized light has apple green birefringence, based on the molecule being in an antiparallel beta-pleated sheet.
  • Note: non-amyloid related green birefringence can occur due to excess dye retained by the tissue
Microscopic (histologic) images

Images hosted on other servers:

Medullary carcinoma of thyroid gland-staining lower right

Amyloid in adrenal gland

Primary localized laryngeal amyloidosis (polarized light-fig F)

Amyloid tumor of breast - fig 1: coarse calcifications of right breast; 2: H&E; 3: Congo red staining; 4: Congo red under polarized light

Images hosted on

Cardiac amyloidosis under polarized light